In marine vessels and other applications, it is typically desirable to provide a steady, reliable electric power source that is suitable for operating relatively sensitive electronic equipment as well as other, more robust, electrical devices.
Medium-sized and large commercial and/or recreational watercraft often incorporate one or more on-board auxiliary diesel engines that drive one or more electric generators to produce necessary electric power for the electrical and electronic equipment on board the vessel that are separate from the main engine system. An advantage of an independent generator system is that it can provide electrical power to the vessel, even when the main engine is not operating. However, the disadvantage of such conventional systems that require one or more auxiliary engines is that they increase fuel consumption and costs; increase the emission of hydrocarbons and other combustion byproducts to the environment; incur additional costs associated with the manufacturing, installation and maintenance of the auxiliary engines; and require the dedication of space on the vessel to the auxiliary diesel engines.
Alternatively, it is known that electric power may be generated using a shaft-driven generator driven directly by the vessel's main engine. A direct-drive system can produce electric power very economically and with relatively low additional effluent of hydrocarbon to the environment. However, to produce a stable electrical power output a direct-drive electrical generator system requires operation of the main engine for power, and at a constant speed, and is therefore only applicable to a few types of vessels.
A present inventor has previously disclosed a system that provides a hydraulic drive that variably connects a power generator to a vessel main engine in U.S. patent application Ser. No. 09/801,049, which is hereby expressly incorporated by reference in its entirety. The system described in the reference application drives a generator from the main engine via a variable output hydraulic pump that is fluidly connected to a constant volume hydraulic motor, wherein the hydraulic pump controller relies only on the frequency deviation on the generator output for controlling the oil quantity from the hydraulic pump. If the output power frequency is too low, the hydraulic pump output is increased, and if the output power frequency is too high, the hydraulic pump output is decreased. In practice, however, the system disclosed in this prior application did not provide sufficient real-time control of the generator speed over the necessary range of main engine speed variations to produce a sufficiently stable power output to accommodate modern electronic equipment.
Therefore, there remains a need for a power generator system suitable for use on a marine vessel that powers the generator by the vessel main engine with improved control of the speed of the generator.